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                        自述
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                            <b>1.</b>
                        
                        介绍
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                            <b>1.1.</b>
                        
                        动机
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                            <b>1.2.</b>
                        
                        核心概念
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                            <b>1.3.</b>
                        
                        三大原则
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                            <b>1.4.</b>
                        
                        先前技术
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                            <b>1.5.</b>
                        
                        生态系统
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                            <b>1.6.</b>
                        
                        示例
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                            <b>2.</b>
                        
                        基础
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                            <b>2.1.</b>
                        
                        Action
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                            <b>2.2.</b>
                        
                        Reducer
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                            <b>2.3.</b>
                        
                        Store
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                            <b>2.4.</b>
                        
                        数据流
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                            <b>2.5.</b>
                        
                        搭配 React
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                            <b>2.6.</b>
                        
                        示例：Todo List
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                            <b>3.</b>
                        
                        高级
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                            <b>3.1.</b>
                        
                        异步 Action
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                            <b>3.2.</b>
                        
                        异步数据流
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                            <b>3.3.</b>
                        
                        Middleware
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                            <b>3.4.</b>
                        
                        搭配 React Router
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                            <b>3.5.</b>
                        
                        示例：Reddit API
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                            <b>3.6.</b>
                        
                        下一步
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                            <b>4.</b>
                        
                        技巧
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                            <b>4.1.</b>
                        
                        迁移到 Redux
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        <li class="chapter " data-level="4.2" data-path="docs/recipes/UsingObjectSpreadOperator.html">
            
                
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                            <b>4.2.</b>
                        
                        使用对象展开运算符
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        <li class="chapter " data-level="4.3" data-path="docs/recipes/ReducingBoilerplate.html">
            
                
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                            <b>4.3.</b>
                        
                        减少样板代码
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        <li class="chapter " data-level="4.4" data-path="docs/recipes/ServerRendering.html">
            
                
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                            <b>4.4.</b>
                        
                        服务端渲染
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                            <b>4.5.</b>
                        
                        编写测试
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        <li class="chapter " data-level="4.6" data-path="docs/recipes/ComputingDerivedData.html">
            
                
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                            <b>4.6.</b>
                        
                        计算衍生数据
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        <li class="chapter " data-level="4.7" data-path="docs/recipes/ImplementingUndoHistory.html">
            
                
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                            <b>4.7.</b>
                        
                        实现撤销重做
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        <li class="chapter " data-level="4.8" data-path="docs/recipes/IsolatingSubapps.html">
            
                
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                            <b>4.8.</b>
                        
                        子应用隔离
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        <li class="chapter " data-level="4.9" data-path="docs/recipes/StructuringReducers.html">
            
                
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                            <b>4.9.</b>
                        
                        组织 Reducer
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        <li class="chapter " data-level="4.9.1" data-path="docs/recipes/reducers/PrerequisiteConcepts.html">
            
                
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                            <b>4.9.1.</b>
                        
                        Reducer 基础概念
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        <li class="chapter " data-level="4.9.2" data-path="docs/recipes/reducers/BasicReducerStructure.html">
            
                
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                            <b>4.9.2.</b>
                        
                        Reducer 基础结构
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        <li class="chapter " data-level="4.9.3" data-path="docs/recipes/reducers/SplittingReducerLogic.html">
            
                
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                            <b>4.9.3.</b>
                        
                        Reducer 逻辑拆分
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        </li>
    
        <li class="chapter " data-level="4.9.4" data-path="docs/recipes/reducers/RefactoringReducersExample.html">
            
                
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                            <b>4.9.4.</b>
                        
                        Reducer 重构示例
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        <li class="chapter " data-level="4.9.5" data-path="docs/recipes/reducers/UsingCombineReducers.html">
            
                
                    <a href="../../docs/recipes/reducers/UsingCombineReducers.html">
                
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                            <b>4.9.5.</b>
                        
                        `combineReducers` 用法
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        <li class="chapter " data-level="4.9.6" data-path="docs/recipes/reducers/BeyondCombineReducers.html">
            
                
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                            <b>4.9.6.</b>
                        
                        `combineReducers` 进阶
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        </li>
    
        <li class="chapter " data-level="4.9.7" data-path="docs/recipes/reducers/NormalizingStateShape.html">
            
                
                    <a href="../../docs/recipes/reducers/NormalizingStateShape.html">
                
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                            <b>4.9.7.</b>
                        
                        State 范式化
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="4.9.8" data-path="docs/recipes/reducers/UpdatingNormalizedData.html">
            
                
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                            <b>4.9.8.</b>
                        
                        管理范式化数据
                    </a>
            
            
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        <li class="chapter " data-level="4.9.9" data-path="docs/recipes/reducers/ReusingReducerLogic.html">
            
                
                    <a href="../../docs/recipes/reducers/ReusingReducerLogic.html">
                
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                            <b>4.9.9.</b>
                        
                        Reducer 逻辑复用
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="4.9.10" data-path="docs/recipes/reducers/ImmutableUpdatePatterns.html">
            
                
                    <a href="../../docs/recipes/reducers/ImmutableUpdatePatterns.html">
                
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                            <b>4.9.10.</b>
                        
                        不可变更新模式
                    </a>
            
            
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        <li class="chapter " data-level="4.9.11" data-path="docs/recipes/reducers/InitializingState.html">
            
                
                    <a href="../../docs/recipes/reducers/InitializingState.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>4.9.11.</b>
                        
                        初始化 State
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="5" data-path="docs/FAQ.html">
            
                
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                            <b>5.</b>
                        
                        常见问题
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            <ul class="articles">
                
    
        <li class="chapter " data-level="5.1" data-path="docs/faq/General.html">
            
                
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                            <b>5.1.</b>
                        
                        综合
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        <li class="chapter " data-level="5.2" data-path="docs/faq/Reducers.html">
            
                
                    <a href="../../docs/faq/Reducers.html">
                
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                            <b>5.2.</b>
                        
                        Reducer
                    </a>
            
            
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        <li class="chapter " data-level="5.3" data-path="docs/faq/OrganizingState.html">
            
                
                    <a href="../../docs/faq/OrganizingState.html">
                
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                            <b>5.3.</b>
                        
                        组织 State
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.4" data-path="docs/faq/StoreSetup.html">
            
                
                    <a href="../../docs/faq/StoreSetup.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.4.</b>
                        
                        创建 Store
                    </a>
            
            
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        <li class="chapter " data-level="5.5" data-path="docs/faq/Actions.html">
            
                
                    <a href="../../docs/faq/Actions.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.5.</b>
                        
                        Action
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.6" data-path="docs/faq/CodeStructure.html">
            
                
                    <a href="../../docs/faq/CodeStructure.html">
                
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                            <b>5.6.</b>
                        
                        代码结构
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="5.7" data-path="docs/faq/Performance.html">
            
                
                    <a href="../../docs/faq/Performance.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.7.</b>
                        
                        性能
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        </li>
    
        <li class="chapter " data-level="5.8" data-path="docs/faq/ReactRedux.html">
            
                
                    <a href="../../docs/faq/ReactRedux.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.8.</b>
                        
                        React Redux
                    </a>
            
            
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        <li class="chapter " data-level="5.9" data-path="docs/faq/Miscellaneous.html">
            
                
                    <a href="../../docs/faq/Miscellaneous.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>5.9.</b>
                        
                        其它
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="6" data-path="docs/Troubleshooting.html">
            
                
                    <a href="../../docs/Troubleshooting.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>6.</b>
                        
                        排错
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="7" data-path="docs/Glossary.html">
            
                
                    <a href="../../docs/Glossary.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>7.</b>
                        
                        词汇表
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8" data-path="docs/api/index.html">
            
                
                    <a href="../../docs/api/index.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.</b>
                        
                        API 文档
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="8.1" data-path="docs/api/createStore.html">
            
                
                    <a href="../../docs/api/createStore.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.1.</b>
                        
                        createStore
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.2" data-path="docs/api/Store.html">
            
                
                    <a href="../../docs/api/Store.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.2.</b>
                        
                        Store
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.3" data-path="docs/api/combineReducers.html">
            
                
                    <a href="../../docs/api/combineReducers.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.3.</b>
                        
                        combineReducers
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.4" data-path="docs/api/applyMiddleware.html">
            
                
                    <a href="../../docs/api/applyMiddleware.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.4.</b>
                        
                        applyMiddleware
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.5" data-path="docs/api/bindActionCreators.html">
            
                
                    <a href="../../docs/api/bindActionCreators.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.5.</b>
                        
                        bindActionCreators
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="8.6" data-path="docs/api/compose.html">
            
                
                    <a href="../../docs/api/compose.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>8.6.</b>
                        
                        compose
                    </a>
            
            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="9" data-path="docs/react-redux/index.html">
            
                
                    <a href="../../docs/react-redux/index.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>9.</b>
                        
                        react-redux 文档
                    </a>
            
            
            <ul class="articles">
                
    
        <li class="chapter " data-level="9.1" data-path="docs/react-redux/api.html">
            
                
                    <a href="../../docs/react-redux/api.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>9.1.</b>
                        
                        API
                    </a>
            
            
        </li>
    
        <li class="chapter " data-level="9.2" data-path="docs/react-redux/troubleshooting.html">
            
                
                    <a href="../../docs/react-redux/troubleshooting.html">
                
                        <i class="fa fa-check"></i>
                        
                            <b>9.2.</b>
                        
                        排错
                    </a>
            
            
        </li>
    

            </ul>
            
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        <i class="fa fa-circle-o-notch fa-spin"></i>
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                    <section class="normal" id="section-">
                    
                        <a id="edit-link" href="https://github.com/camsong/redux-in-chinese/tree/master/docs/basics/Reducers.md" class="btn fa fa-edit pull-left">&#xA0;&#xA0;&#x5F00;&#x59CB;&#x7EA0;&#x9519;</a><h1 id="reducer">Reducer</h1>
<p><a href="Actions.html">Action</a> &#x53EA;&#x662F;&#x63CF;&#x8FF0;&#x4E86;<strong>&#x6709;&#x4E8B;&#x60C5;&#x53D1;&#x751F;&#x4E86;</strong>&#x8FD9;&#x4E00;&#x4E8B;&#x5B9E;&#xFF0C;&#x5E76;&#x6CA1;&#x6709;&#x6307;&#x660E;&#x5E94;&#x7528;&#x5982;&#x4F55;&#x66F4;&#x65B0; state&#x3002;&#x800C;&#x8FD9;&#x6B63;&#x662F; reducer &#x8981;&#x505A;&#x7684;&#x4E8B;&#x60C5;&#x3002;</p>
<h2 id="%E8%AE%BE%E8%AE%A1-state-%E7%BB%93%E6%9E%84">&#x8BBE;&#x8BA1; State &#x7ED3;&#x6784;</h2>
<p>&#x5728; Redux &#x5E94;&#x7528;&#x4E2D;&#xFF0C;&#x6240;&#x6709;&#x7684; state &#x90FD;&#x88AB;&#x4FDD;&#x5B58;&#x5728;&#x4E00;&#x4E2A;&#x5355;&#x4E00;&#x5BF9;&#x8C61;&#x4E2D;&#x3002;&#x5EFA;&#x8BAE;&#x5728;&#x5199;&#x4EE3;&#x7801;&#x524D;&#x5148;&#x60F3;&#x4E00;&#x4E0B;&#x8FD9;&#x4E2A;&#x5BF9;&#x8C61;&#x7684;&#x7ED3;&#x6784;&#x3002;&#x5982;&#x4F55;&#x624D;&#x80FD;&#x4EE5;&#x6700;&#x7B80;&#x7684;&#x5F62;&#x5F0F;&#x628A;&#x5E94;&#x7528;&#x7684; state &#x7528;&#x5BF9;&#x8C61;&#x63CF;&#x8FF0;&#x51FA;&#x6765;&#xFF1F;</p>
<p>&#x4EE5; todo &#x5E94;&#x7528;&#x4E3A;&#x4F8B;&#xFF0C;&#x9700;&#x8981;&#x4FDD;&#x5B58;&#x4E24;&#x79CD;&#x4E0D;&#x540C;&#x7684;&#x6570;&#x636E;&#xFF1A;</p>
<ul>
<li>&#x5F53;&#x524D;&#x9009;&#x4E2D;&#x7684;&#x4EFB;&#x52A1;&#x8FC7;&#x6EE4;&#x6761;&#x4EF6;&#xFF1B;</li>
<li>&#x5B8C;&#x6574;&#x7684;&#x4EFB;&#x52A1;&#x5217;&#x8868;&#x3002;</li>
</ul>
<p>&#x901A;&#x5E38;&#xFF0C;&#x8FD9;&#x4E2A; state &#x6811;&#x8FD8;&#x9700;&#x8981;&#x5B58;&#x653E;&#x5176;&#x5B83;&#x4E00;&#x4E9B;&#x6570;&#x636E;&#xFF0C;&#x4EE5;&#x53CA;&#x4E00;&#x4E9B; UI &#x76F8;&#x5173;&#x7684; state&#x3002;&#x8FD9;&#x6837;&#x505A;&#x6CA1;&#x95EE;&#x9898;&#xFF0C;&#x4F46;&#x5C3D;&#x91CF;&#x628A;&#x8FD9;&#x4E9B;&#x6570;&#x636E;&#x4E0E; UI &#x76F8;&#x5173;&#x7684; state &#x5206;&#x5F00;&#x3002;</p>
<pre><code class="lang-js"><span class="token punctuation">{</span>
  visibilityFilter<span class="token punctuation">:</span> <span class="token string">&apos;SHOW_ALL&apos;</span><span class="token punctuation">,</span>
  todos<span class="token punctuation">:</span> <span class="token punctuation">[</span>
    <span class="token punctuation">{</span>
      text<span class="token punctuation">:</span> <span class="token string">&apos;Consider using Redux&apos;</span><span class="token punctuation">,</span>
      completed<span class="token punctuation">:</span> <span class="token keyword">true</span><span class="token punctuation">,</span>
    <span class="token punctuation">}</span><span class="token punctuation">,</span>
    <span class="token punctuation">{</span>
      text<span class="token punctuation">:</span> <span class="token string">&apos;Keep all state in a single tree&apos;</span><span class="token punctuation">,</span>
      completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">]</span>
<span class="token punctuation">}</span>
</code></pre>
<blockquote>
<h5 id="%E5%A4%84%E7%90%86-reducer-%E5%85%B3%E7%B3%BB%E6%97%B6%E7%9A%84%E6%B3%A8%E6%84%8F%E4%BA%8B%E9%A1%B9">&#x5904;&#x7406; Reducer &#x5173;&#x7CFB;&#x65F6;&#x7684;&#x6CE8;&#x610F;&#x4E8B;&#x9879;</h5>
<p>&#x5F00;&#x53D1;&#x590D;&#x6742;&#x7684;&#x5E94;&#x7528;&#x65F6;&#xFF0C;&#x4E0D;&#x53EF;&#x907F;&#x514D;&#x4F1A;&#x6709;&#x4E00;&#x4E9B;&#x6570;&#x636E;&#x76F8;&#x4E92;&#x5F15;&#x7528;&#x3002;&#x5EFA;&#x8BAE;&#x4F60;&#x5C3D;&#x53EF;&#x80FD;&#x5730;&#x628A; state &#x8303;&#x5F0F;&#x5316;&#xFF0C;&#x4E0D;&#x5B58;&#x5728;&#x5D4C;&#x5957;&#x3002;&#x628A;&#x6240;&#x6709;&#x6570;&#x636E;&#x653E;&#x5230;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x91CC;&#xFF0C;&#x6BCF;&#x4E2A;&#x6570;&#x636E;&#x4EE5; ID &#x4E3A;&#x4E3B;&#x952E;&#xFF0C;&#x4E0D;&#x540C;&#x5B9E;&#x4F53;&#x6216;&#x5217;&#x8868;&#x95F4;&#x901A;&#x8FC7; ID &#x76F8;&#x4E92;&#x5F15;&#x7528;&#x6570;&#x636E;&#x3002;&#x628A;&#x5E94;&#x7528;&#x7684; state &#x60F3;&#x50CF;&#x6210;&#x6570;&#x636E;&#x5E93;&#x3002;&#x8FD9;&#x79CD;&#x65B9;&#x6CD5;&#x5728; <a href="https://github.com/gaearon/normalizr" target="_blank">normalizr</a> &#x6587;&#x6863;&#x91CC;&#x6709;&#x8BE6;&#x7EC6;&#x9610;&#x8FF0;&#x3002;&#x4F8B;&#x5982;&#xFF0C;&#x5B9E;&#x9645;&#x5F00;&#x53D1;&#x4E2D;&#xFF0C;&#x5728; state &#x91CC;&#x540C;&#x65F6;&#x5B58;&#x653E; <code>todosById<span class="token punctuation">:</span> <span class="token punctuation">{</span> id <span class="token operator">-</span><span class="token operator">&gt;</span> todo <span class="token punctuation">}</span></code> &#x548C; <code>todos<span class="token punctuation">:</span> array<span class="token operator">&lt;</span>id<span class="token operator">&gt;</span></code> &#x662F;&#x6BD4;&#x8F83;&#x597D;&#x7684;&#x65B9;&#x5F0F;&#xFF0C;&#x672C;&#x6587;&#x4E2D;&#x4E3A;&#x4E86;&#x4FDD;&#x6301;&#x793A;&#x4F8B;&#x7B80;&#x5355;&#x6CA1;&#x6709;&#x8FD9;&#x6837;&#x5904;&#x7406;&#x3002;</p>
</blockquote>
<h2 id="action-%E5%A4%84%E7%90%86">Action &#x5904;&#x7406;</h2>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x5DF2;&#x7ECF;&#x786E;&#x5B9A;&#x4E86; state &#x5BF9;&#x8C61;&#x7684;&#x7ED3;&#x6784;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x5F00;&#x59CB;&#x5F00;&#x53D1; reducer&#x3002;reducer &#x5C31;&#x662F;&#x4E00;&#x4E2A;&#x7EAF;&#x51FD;&#x6570;&#xFF0C;&#x63A5;&#x6536;&#x65E7;&#x7684; state &#x548C; action&#xFF0C;&#x8FD4;&#x56DE;&#x65B0;&#x7684; state&#x3002;</p>
<pre><code class="lang-js"><span class="token punctuation">(</span>previousState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> newState
</code></pre>
<p>&#x4E4B;&#x6240;&#x4EE5;&#x79F0;&#x4F5C; reducer &#x662F;&#x56E0;&#x4E3A;&#x5B83;&#x5C06;&#x88AB;&#x4F20;&#x9012;&#x7ED9; <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce" target="_blank"><code>Array<span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span>reducer<span class="token punctuation">,</span> <span class="token operator">?</span>initialValue<span class="token punctuation">)</span></code></a> &#x65B9;&#x6CD5;&#x3002;&#x4FDD;&#x6301; reducer &#x7EAF;&#x51C0;&#x975E;&#x5E38;&#x91CD;&#x8981;&#x3002;<strong>&#x6C38;&#x8FDC;&#x4E0D;&#x8981;</strong>&#x5728; reducer &#x91CC;&#x505A;&#x8FD9;&#x4E9B;&#x64CD;&#x4F5C;&#xFF1A;</p>
<ul>
<li>&#x4FEE;&#x6539;&#x4F20;&#x5165;&#x53C2;&#x6570;&#xFF1B;</li>
<li>&#x6267;&#x884C;&#x6709;&#x526F;&#x4F5C;&#x7528;&#x7684;&#x64CD;&#x4F5C;&#xFF0C;&#x5982; API &#x8BF7;&#x6C42;&#x548C;&#x8DEF;&#x7531;&#x8DF3;&#x8F6C;&#xFF1B;</li>
<li>&#x8C03;&#x7528;&#x975E;&#x7EAF;&#x51FD;&#x6570;&#xFF0C;&#x5982; <code>Date<span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code> &#x6216; <code>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code>&#x3002;</li>
</ul>
<p>&#x5728;<a href="../advanced/index.html">&#x9AD8;&#x7EA7;&#x7BC7;</a>&#x91CC;&#x4F1A;&#x4ECB;&#x7ECD;&#x5982;&#x4F55;&#x6267;&#x884C;&#x6709;&#x526F;&#x4F5C;&#x7528;&#x7684;&#x64CD;&#x4F5C;&#x3002;&#x73B0;&#x5728;&#x53EA;&#x9700;&#x8981;&#x8C28;&#x8BB0; reducer &#x4E00;&#x5B9A;&#x8981;&#x4FDD;&#x6301;&#x7EAF;&#x51C0;&#x3002;<strong>&#x53EA;&#x8981;&#x4F20;&#x5165;&#x53C2;&#x6570;&#x76F8;&#x540C;&#xFF0C;&#x8FD4;&#x56DE;&#x8BA1;&#x7B97;&#x5F97;&#x5230;&#x7684;&#x4E0B;&#x4E00;&#x4E2A; state &#x5C31;&#x4E00;&#x5B9A;&#x76F8;&#x540C;&#x3002;&#x6CA1;&#x6709;&#x7279;&#x6B8A;&#x60C5;&#x51B5;&#x3001;&#x6CA1;&#x6709;&#x526F;&#x4F5C;&#x7528;&#xFF0C;&#x6CA1;&#x6709; API &#x8BF7;&#x6C42;&#x3001;&#x6CA1;&#x6709;&#x53D8;&#x91CF;&#x4FEE;&#x6539;&#xFF0C;&#x5355;&#x7EAF;&#x6267;&#x884C;&#x8BA1;&#x7B97;&#x3002;</strong></p>
<p>&#x660E;&#x767D;&#x4E86;&#x8FD9;&#x4E9B;&#x4E4B;&#x540E;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x5F00;&#x59CB;&#x7F16;&#x5199; reducer&#xFF0C;&#x5E76;&#x8BA9;&#x5B83;&#x6765;&#x5904;&#x7406;&#x4E4B;&#x524D;&#x5B9A;&#x4E49;&#x8FC7;&#x7684; <a href="Actions.html">action</a>&#x3002;</p>
<p>&#x6211;&#x4EEC;&#x5C06;&#x4EE5;&#x6307;&#x5B9A; state &#x7684;&#x521D;&#x59CB;&#x72B6;&#x6001;&#x4F5C;&#x4E3A;&#x5F00;&#x59CB;&#x3002;Redux &#x9996;&#x6B21;&#x6267;&#x884C;&#x65F6;&#xFF0C;state &#x4E3A; <code>undefined</code>&#xFF0C;&#x6B64;&#x65F6;&#x6211;&#x4EEC;&#x53EF;&#x501F;&#x673A;&#x8BBE;&#x7F6E;&#x5E76;&#x8FD4;&#x56DE;&#x5E94;&#x7528;&#x7684;&#x521D;&#x59CB; state&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> VisibilityFilters <span class="token punctuation">}</span> from <span class="token string">&apos;./actions&apos;</span>

<span class="token keyword">const</span> initialState <span class="token operator">=</span> <span class="token punctuation">{</span>
  visibilityFilter<span class="token punctuation">:</span> VisibilityFilters<span class="token punctuation">.</span>SHOW_ALL<span class="token punctuation">,</span>
  todos<span class="token punctuation">:</span> <span class="token punctuation">[</span><span class="token punctuation">]</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> state <span class="token operator">===</span> <span class="token string">&apos;undefined&apos;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> initialState
  <span class="token punctuation">}</span>

  <span class="token comment" spellcheck="true">// &#x8FD9;&#x91CC;&#x6682;&#x4E0D;&#x5904;&#x7406;&#x4EFB;&#x4F55; action&#xFF0C;</span>
  <span class="token comment" spellcheck="true">// &#x4EC5;&#x8FD4;&#x56DE;&#x4F20;&#x5165;&#x7684; state&#x3002;</span>
  <span class="token keyword">return</span> state
<span class="token punctuation">}</span>
</code></pre>
<p>&#x8FD9;&#x91CC;&#x4E00;&#x4E2A;&#x6280;&#x5DE7;&#x662F;&#x4F7F;&#x7528; <a href="https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/default_parameters" target="_blank">ES6 &#x53C2;&#x6570;&#x9ED8;&#x8BA4;&#x503C;&#x8BED;&#x6CD5;</a> &#x6765;&#x7CBE;&#x7B80;&#x4EE3;&#x7801;&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> initialState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token comment" spellcheck="true">// &#x8FD9;&#x91CC;&#x6682;&#x4E0D;&#x5904;&#x7406;&#x4EFB;&#x4F55; action&#xFF0C;</span>
  <span class="token comment" spellcheck="true">// &#x4EC5;&#x8FD4;&#x56DE;&#x4F20;&#x5165;&#x7684; state&#x3002;</span>
  <span class="token keyword">return</span> state
<span class="token punctuation">}</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x53EF;&#x4EE5;&#x5904;&#x7406; <code>SET_VISIBILITY_FILTER</code>&#x3002;&#x9700;&#x8981;&#x505A;&#x7684;&#x53EA;&#x662F;&#x6539;&#x53D8; state &#x4E2D;&#x7684; <code>visibilityFilter</code>&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> initialState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        visibilityFilter<span class="token punctuation">:</span> action<span class="token punctuation">.</span>filter
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x6CE8;&#x610F;:</p>
<ol>
<li><p><strong>&#x4E0D;&#x8981;&#x4FEE;&#x6539; <code>state</code>&#x3002;</strong> &#x4F7F;&#x7528; <a href="https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign" target="_blank"><code>Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></a> &#x65B0;&#x5EFA;&#x4E86;&#x4E00;&#x4E2A;&#x526F;&#x672C;&#x3002;&#x4E0D;&#x80FD;&#x8FD9;&#x6837;&#x4F7F;&#x7528; <code>Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span>state<span class="token punctuation">,</span> <span class="token punctuation">{</span> visibilityFilter<span class="token punctuation">:</span> action<span class="token punctuation">.</span>filter <span class="token punctuation">}</span><span class="token punctuation">)</span></code>&#xFF0C;&#x56E0;&#x4E3A;&#x5B83;&#x4F1A;&#x6539;&#x53D8;&#x7B2C;&#x4E00;&#x4E2A;&#x53C2;&#x6570;&#x7684;&#x503C;&#x3002;&#x4F60;<strong>&#x5FC5;&#x987B;</strong>&#x628A;&#x7B2C;&#x4E00;&#x4E2A;&#x53C2;&#x6570;&#x8BBE;&#x7F6E;&#x4E3A;&#x7A7A;&#x5BF9;&#x8C61;&#x3002;&#x4F60;&#x4E5F;&#x53EF;&#x4EE5;&#x5F00;&#x542F;&#x5BF9;ES7&#x63D0;&#x6848;<a href="../recipes/UsingObjectSpreadOperator.html">&#x5BF9;&#x8C61;&#x5C55;&#x5F00;&#x8FD0;&#x7B97;&#x7B26;</a>&#x7684;&#x652F;&#x6301;, &#x4ECE;&#x800C;&#x4F7F;&#x7528; <code><span class="token punctuation">{</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">,</span> <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>newState <span class="token punctuation">}</span></code> &#x8FBE;&#x5230;&#x76F8;&#x540C;&#x7684;&#x76EE;&#x7684;&#x3002;</p>
</li>
<li><p><strong>&#x5728; <code><span class="token keyword">default</span></code> &#x60C5;&#x51B5;&#x4E0B;&#x8FD4;&#x56DE;&#x65E7;&#x7684; <code>state</code>&#x3002;</strong>&#x9047;&#x5230;&#x672A;&#x77E5;&#x7684; action &#x65F6;&#xFF0C;&#x4E00;&#x5B9A;&#x8981;&#x8FD4;&#x56DE;&#x65E7;&#x7684; <code>state</code>&#x3002;</p>
</li>
</ol>
<blockquote>
<h5 id="-object-assign-%E9%A1%BB%E7%9F%A5"><code>Object<span class="token punctuation">.</span>assign</code> &#x987B;&#x77E5;</h5>
<p><a href="https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/assign" target="_blank"><code>Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></a> &#x662F; ES6 &#x7279;&#x6027;&#xFF0C;&#x4F46;&#x591A;&#x6570;&#x6D4F;&#x89C8;&#x5668;&#x5E76;&#x4E0D;&#x652F;&#x6301;&#x3002;&#x4F60;&#x8981;&#x4E48;&#x4F7F;&#x7528; polyfill&#xFF0C;<a href="https://github.com/babel-plugins/babel-plugin-object-assign" target="_blank">Babel &#x63D2;&#x4EF6;</a>&#xFF0C;&#x6216;&#x8005;&#x4F7F;&#x7528;&#x5176;&#x5B83;&#x5E93;&#x5982; <a href="https://lodash.com/docs#assign" target="_blank"><code>_<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></a> &#x63D0;&#x4F9B;&#x7684;&#x5E2E;&#x52A9;&#x65B9;&#x6CD5;&#x3002;</p>
<h5 id="-switch-%E5%92%8C%E6%A0%B7%E6%9D%BF%E4%BB%A3%E7%A0%81%E9%A1%BB%E7%9F%A5"><code><span class="token keyword">switch</span></code> &#x548C;&#x6837;&#x677F;&#x4EE3;&#x7801;&#x987B;&#x77E5;</h5>
<p><code><span class="token keyword">switch</span></code> &#x8BED;&#x53E5;&#x5E76;&#x4E0D;&#x662F;&#x4E25;&#x683C;&#x610F;&#x4E49;&#x4E0A;&#x7684;&#x6837;&#x677F;&#x4EE3;&#x7801;&#x3002;Flux &#x4E2D;&#x771F;&#x5B9E;&#x7684;&#x6837;&#x677F;&#x4EE3;&#x7801;&#x662F;&#x6982;&#x5FF5;&#x6027;&#x7684;&#xFF1A;&#x66F4;&#x65B0;&#x5FC5;&#x987B;&#x8981;&#x53D1;&#x9001;&#x3001;Store &#x5FC5;&#x987B;&#x8981;&#x6CE8;&#x518C;&#x5230; Dispatcher&#x3001;Store &#x5FC5;&#x987B;&#x662F;&#x5BF9;&#x8C61;&#xFF08;&#x5F00;&#x53D1;&#x540C;&#x6784;&#x5E94;&#x7528;&#x65F6;&#x53D8;&#x5F97;&#x975E;&#x5E38;&#x590D;&#x6742;&#xFF09;&#x3002;&#x4E3A;&#x4E86;&#x89E3;&#x51B3;&#x8FD9;&#x4E9B;&#x95EE;&#x9898;&#xFF0C;Redux &#x653E;&#x5F03;&#x4E86; event emitters&#xFF08;&#x4E8B;&#x4EF6;&#x53D1;&#x9001;&#x5668;&#xFF09;&#xFF0C;&#x8F6C;&#x800C;&#x4F7F;&#x7528;&#x7EAF; reducer&#x3002;</p>
<p>&#x5F88;&#x4E0D;&#x5E78;&#x5230;&#x73B0;&#x5728;&#x4E3A;&#x6B62;&#xFF0C;&#x8FD8;&#x6709;&#x5F88;&#x591A;&#x4EBA;&#x5B58;&#x5728;&#x4E00;&#x4E2A;&#x8BEF;&#x533A;&#xFF1A;&#x6839;&#x636E;&#x6587;&#x6863;&#x4E2D;&#x662F;&#x5426;&#x4F7F;&#x7528; <code><span class="token keyword">switch</span></code> &#x6765;&#x51B3;&#x5B9A;&#x662F;&#x5426;&#x4F7F;&#x7528;&#x5B83;&#x3002;&#x5982;&#x679C;&#x4F60;&#x4E0D;&#x559C;&#x6B22; <code><span class="token keyword">switch</span></code>&#xFF0C;&#x5B8C;&#x5168;&#x53EF;&#x4EE5;&#x81EA;&#x5B9A;&#x4E49;&#x4E00;&#x4E2A; <code>createReducer</code> &#x51FD;&#x6570;&#x6765;&#x63A5;&#x6536;&#x4E00;&#x4E2A;&#x4E8B;&#x4EF6;&#x5904;&#x7406;&#x51FD;&#x6570;&#x5217;&#x8868;&#xFF0C;&#x53C2;&#x7167;<a href="../recipes/ReducingBoilerplate.html#reducers">&quot;&#x51CF;&#x5C11;&#x6837;&#x677F;&#x4EE3;&#x7801;&quot;</a>&#x3002;</p>
</blockquote>
<h2 id="%E5%A4%84%E7%90%86%E5%A4%9A%E4%B8%AA-action">&#x5904;&#x7406;&#x591A;&#x4E2A; action</h2>
<p>&#x8FD8;&#x6709;&#x4E24;&#x4E2A; action &#x9700;&#x8981;&#x5904;&#x7406;&#x3002;&#x8BA9;&#x6211;&#x4EEC;&#x5148;&#x5904;&#x7406; <code>ADD_TODO</code>&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> initialState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        visibilityFilter<span class="token punctuation">:</span> action<span class="token punctuation">.</span>filter
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        todos<span class="token punctuation">:</span> <span class="token punctuation">[</span>
          <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>todos<span class="token punctuation">,</span>
          <span class="token punctuation">{</span>
            text<span class="token punctuation">:</span> action<span class="token punctuation">.</span>text<span class="token punctuation">,</span>
            completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
          <span class="token punctuation">}</span>
        <span class="token punctuation">]</span>
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x5982;&#x4E0A;&#xFF0C;&#x4E0D;&#x76F4;&#x63A5;&#x4FEE;&#x6539; <code>state</code> &#x4E2D;&#x7684;&#x5B57;&#x6BB5;&#xFF0C;&#x800C;&#x662F;&#x8FD4;&#x56DE;&#x65B0;&#x5BF9;&#x8C61;&#x3002;&#x65B0;&#x7684; <code>todos</code> &#x5BF9;&#x8C61;&#x5C31;&#x76F8;&#x5F53;&#x4E8E;&#x65E7;&#x7684; <code>todos</code> &#x5728;&#x672B;&#x5C3E;&#x52A0;&#x4E0A;&#x65B0;&#x5EFA;&#x7684; todo&#x3002;&#x800C;&#x8FD9;&#x4E2A;&#x65B0;&#x7684; todo &#x53C8;&#x662F;&#x57FA;&#x4E8E; action &#x4E2D;&#x7684;&#x6570;&#x636E;&#x521B;&#x5EFA;&#x7684;&#x3002;</p>
<p>&#x6700;&#x540E;&#xFF0C;<code>TOGGLE_TODO</code> &#x7684;&#x5B9E;&#x73B0;&#x4E5F;&#x5F88;&#x597D;&#x7406;&#x89E3;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
  <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
    todos<span class="token punctuation">:</span> state<span class="token punctuation">.</span>todos<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span>todo<span class="token punctuation">,</span> index<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>index <span class="token operator">===</span> action<span class="token punctuation">.</span>index<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> todo<span class="token punctuation">,</span> <span class="token punctuation">{</span>
          completed<span class="token punctuation">:</span> <span class="token operator">!</span>todo<span class="token punctuation">.</span>completed
        <span class="token punctuation">}</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span>
      <span class="token keyword">return</span> todo
    <span class="token punctuation">}</span><span class="token punctuation">)</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x9700;&#x8981;&#x4FEE;&#x6539;&#x6570;&#x7EC4;&#x4E2D;&#x6307;&#x5B9A;&#x7684;&#x6570;&#x636E;&#x9879;&#x800C;&#x53C8;&#x4E0D;&#x5E0C;&#x671B;&#x5BFC;&#x81F4;<strong>&#x7A81;&#x53D8;</strong>, &#x56E0;&#x6B64;&#x6211;&#x4EEC;&#x7684;&#x505A;&#x6CD5;&#x662F;&#x5728;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;&#x65B0;&#x7684;&#x6570;&#x7EC4;&#x540E;, &#x5C06;&#x90A3;&#x4E9B;&#x65E0;&#x9700;&#x4FEE;&#x6539;&#x7684;&#x9879;&#x539F;&#x5C01;&#x4E0D;&#x52A8;&#x79FB;&#x5165;, &#x63A5;&#x7740;&#x5BF9;&#x9700;&#x4FEE;&#x6539;&#x7684;&#x9879;&#x7528;&#x65B0;&#x751F;&#x6210;&#x7684;&#x5BF9;&#x8C61;&#x66FF;&#x6362;&#x3002;(&#x8BD1;&#x8005;&#x6CE8;&#xFF1A;Javascript&#x4E2D;&#x7684;&#x5BF9;&#x8C61;&#x5B58;&#x50A8;&#x65F6;&#x5747;&#x662F;&#x7531;&#x503C;&#x548C;&#x6307;&#x5411;&#x503C;&#x7684;&#x5F15;&#x7528;&#x4E24;&#x4E2A;&#x90E8;&#x5206;&#x6784;&#x6210;&#x3002;&#x6B64;&#x5904;<strong>&#x7A81;&#x53D8;</strong>&#x6307;&#x76F4;&#x63A5;&#x4FEE;&#x6539;&#x5F15;&#x7528;&#x6240;&#x6307;&#x5411;&#x7684;&#x503C;, &#x800C;&#x5F15;&#x7528;&#x672C;&#x8EAB;&#x4FDD;&#x6301;&#x4E0D;&#x53D8;&#x3002;) &#x5982;&#x679C;&#x7ECF;&#x5E38;&#x9700;&#x8981;&#x8FD9;&#x7C7B;&#x7684;&#x64CD;&#x4F5C;&#xFF0C;&#x53EF;&#x4EE5;&#x9009;&#x62E9;&#x4F7F;&#x7528;&#x5E2E;&#x52A9;&#x7C7B; <a href="https://facebook.github.io/react/docs/update.html" target="_blank">React-addons-update</a>&#xFF0C;<a href="https://github.com/substantial/updeep" target="_blank">updeep</a>&#xFF0C;&#x6216;&#x8005;&#x4F7F;&#x7528;&#x539F;&#x751F;&#x652F;&#x6301;&#x6DF1;&#x5EA6;&#x66F4;&#x65B0;&#x7684;&#x5E93; <a href="http://facebook.github.io/immutable-js/" target="_blank">Immutable</a>&#x3002;&#x6700;&#x540E;&#xFF0C;&#x65F6;&#x523B;&#x8C28;&#x8BB0;&#x6C38;&#x8FDC;&#x4E0D;&#x8981;&#x5728;&#x514B;&#x9686; <code>state</code> &#x524D;&#x4FEE;&#x6539;&#x5B83;&#x3002;</p>
<h2 id="%E6%8B%86%E5%88%86-reducer">&#x62C6;&#x5206; Reducer</h2>
<p>&#x76EE;&#x524D;&#x7684;&#x4EE3;&#x7801;&#x770B;&#x8D77;&#x6765;&#x6709;&#x4E9B;&#x5197;&#x957F;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> initialState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        visibilityFilter<span class="token punctuation">:</span> action<span class="token punctuation">.</span>filter
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        todos<span class="token punctuation">:</span> <span class="token punctuation">[</span>
          <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>todos<span class="token punctuation">,</span>
          <span class="token punctuation">{</span>
            text<span class="token punctuation">:</span> action<span class="token punctuation">.</span>text<span class="token punctuation">,</span>
            completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
          <span class="token punctuation">}</span>
        <span class="token punctuation">]</span>
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        todos<span class="token punctuation">:</span> state<span class="token punctuation">.</span>todos<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span>todo<span class="token punctuation">,</span> index<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
          <span class="token keyword">if</span><span class="token punctuation">(</span>index <span class="token operator">===</span> action<span class="token punctuation">.</span>index<span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> todo<span class="token punctuation">,</span> <span class="token punctuation">{</span>
              completed<span class="token punctuation">:</span> <span class="token operator">!</span>todo<span class="token punctuation">.</span>completed
            <span class="token punctuation">}</span><span class="token punctuation">)</span>
          <span class="token punctuation">}</span>
          <span class="token keyword">return</span> todo
        <span class="token punctuation">}</span><span class="token punctuation">)</span>
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x80FD;&#x5426;&#x53D8;&#x5F97;&#x66F4;&#x901A;&#x4FD7;&#x6613;&#x61C2;&#xFF1F;&#x8FD9;&#x91CC;&#x7684; <code>todos</code> &#x548C; <code>visibilityFilter</code> &#x7684;&#x66F4;&#x65B0;&#x770B;&#x8D77;&#x6765;&#x662F;&#x76F8;&#x4E92;&#x72EC;&#x7ACB;&#x7684;&#x3002;&#x6709;&#x65F6; state &#x4E2D;&#x7684;&#x5B57;&#x6BB5;&#x662F;&#x76F8;&#x4E92;&#x4F9D;&#x8D56;&#x7684;&#xFF0C;&#x9700;&#x8981;&#x8BA4;&#x771F;&#x8003;&#x8651;&#xFF0C;&#x4F46;&#x5728;&#x8FD9;&#x4E2A;&#x6848;&#x4F8B;&#x4E2D;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x628A; <code>todos</code> &#x66F4;&#x65B0;&#x7684;&#x4E1A;&#x52A1;&#x903B;&#x8F91;&#x62C6;&#x5206;&#x5230;&#x4E00;&#x4E2A;&#x5355;&#x72EC;&#x7684;&#x51FD;&#x6570;&#x91CC;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todos</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> <span class="token punctuation">[</span>
        <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">,</span>
        <span class="token punctuation">{</span>
          text<span class="token punctuation">:</span> action<span class="token punctuation">.</span>text<span class="token punctuation">,</span>
          completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">]</span>
    <span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> state<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span>todo<span class="token punctuation">,</span> index<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>index <span class="token operator">===</span> action<span class="token punctuation">.</span>index<span class="token punctuation">)</span> <span class="token punctuation">{</span>
          <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> todo<span class="token punctuation">,</span> <span class="token punctuation">{</span>
            completed<span class="token punctuation">:</span> <span class="token operator">!</span>todo<span class="token punctuation">.</span>completed
          <span class="token punctuation">}</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> todo
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> initialState<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        visibilityFilter<span class="token punctuation">:</span> action<span class="token punctuation">.</span>filter
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
    <span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> state<span class="token punctuation">,</span> <span class="token punctuation">{</span>
        todos<span class="token punctuation">:</span> <span class="token function">todos</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>todos<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x6CE8;&#x610F; <code>todos</code> &#x4F9D;&#x65E7;&#x63A5;&#x6536; <code>state</code>&#xFF0C;&#x4F46;&#x5B83;&#x53D8;&#x6210;&#x4E86;&#x4E00;&#x4E2A;&#x6570;&#x7EC4;&#xFF01;&#x73B0;&#x5728; <code>todoApp</code> &#x53EA;&#x628A;&#x9700;&#x8981;&#x66F4;&#x65B0;&#x7684;&#x4E00;&#x90E8;&#x5206; state &#x4F20;&#x7ED9; <code>todos</code> &#x51FD;&#x6570;&#xFF0C;<code>todos</code> &#x51FD;&#x6570;&#x81EA;&#x5DF1;&#x786E;&#x5B9A;&#x5982;&#x4F55;&#x66F4;&#x65B0;&#x8FD9;&#x90E8;&#x5206;&#x6570;&#x636E;&#x3002;<strong>&#x8FD9;&#x5C31;&#x662F;&#x6240;&#x8C13;&#x7684; <em>reducer &#x5408;&#x6210;</em>&#xFF0C;&#x5B83;&#x662F;&#x5F00;&#x53D1; Redux &#x5E94;&#x7528;&#x6700;&#x57FA;&#x7840;&#x7684;&#x6A21;&#x5F0F;&#x3002;</strong></p>
<p>&#x4E0B;&#x9762;&#x6DF1;&#x5165;&#x63A2;&#x8BA8;&#x4E00;&#x4E0B;&#x5982;&#x4F55;&#x505A; reducer &#x5408;&#x6210;&#x3002;&#x80FD;&#x5426;&#x62BD;&#x51FA;&#x4E00;&#x4E2A; reducer &#x6765;&#x4E13;&#x95E8;&#x7BA1;&#x7406; <code>visibilityFilter</code>&#xFF1F;&#x5F53;&#x7136;&#x53EF;&#x4EE5;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">visibilityFilter</span><span class="token punctuation">(</span>state <span class="token operator">=</span> SHOW_ALL<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
    <span class="token keyword">return</span> action<span class="token punctuation">.</span>filter
  <span class="token keyword">default</span><span class="token punctuation">:</span>
    <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x5F00;&#x53D1;&#x4E00;&#x4E2A;&#x51FD;&#x6570;&#x6765;&#x505A;&#x4E3A;&#x4E3B; reducer&#xFF0C;&#x5B83;&#x8C03;&#x7528;&#x591A;&#x4E2A;&#x5B50; reducer &#x5206;&#x522B;&#x5904;&#x7406; state &#x4E2D;&#x7684;&#x4E00;&#x90E8;&#x5206;&#x6570;&#x636E;&#xFF0C;&#x7136;&#x540E;&#x518D;&#x628A;&#x8FD9;&#x4E9B;&#x6570;&#x636E;&#x5408;&#x6210;&#x4E00;&#x4E2A;&#x5927;&#x7684;&#x5355;&#x4E00;&#x5BF9;&#x8C61;&#x3002;&#x4E3B; reducer &#x5E76;&#x4E0D;&#x9700;&#x8981;&#x8BBE;&#x7F6E;&#x521D;&#x59CB;&#x5316;&#x65F6;&#x5B8C;&#x6574;&#x7684; state&#x3002;&#x521D;&#x59CB;&#x65F6;&#xFF0C;&#x5982;&#x679C;&#x4F20;&#x5165; <code>undefined</code>, &#x5B50; reducer &#x5C06;&#x8D1F;&#x8D23;&#x8FD4;&#x56DE;&#x5B83;&#x4EEC;&#x7684;&#x9ED8;&#x8BA4;&#x503C;&#x3002;</p>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">todos</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> <span class="token punctuation">[</span>
        <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">,</span>
        <span class="token punctuation">{</span>
          text<span class="token punctuation">:</span> action<span class="token punctuation">.</span>text<span class="token punctuation">,</span>
          completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">]</span>
    <span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> state<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span>todo<span class="token punctuation">,</span> index<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>index <span class="token operator">===</span> action<span class="token punctuation">.</span>index<span class="token punctuation">)</span> <span class="token punctuation">{</span>
          <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> todo<span class="token punctuation">,</span> <span class="token punctuation">{</span>
            completed<span class="token punctuation">:</span> <span class="token operator">!</span>todo<span class="token punctuation">.</span>completed
          <span class="token punctuation">}</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> todo
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">visibilityFilter</span><span class="token punctuation">(</span>state <span class="token operator">=</span> SHOW_ALL<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> action<span class="token punctuation">.</span>filter
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">{</span>
    visibilityFilter<span class="token punctuation">:</span> <span class="token function">visibilityFilter</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>visibilityFilter<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    todos<span class="token punctuation">:</span> <span class="token function">todos</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>todos<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p><strong>&#x6CE8;&#x610F;&#x6BCF;&#x4E2A; reducer &#x53EA;&#x8D1F;&#x8D23;&#x7BA1;&#x7406;&#x5168;&#x5C40; state &#x4E2D;&#x5B83;&#x8D1F;&#x8D23;&#x7684;&#x4E00;&#x90E8;&#x5206;&#x3002;&#x6BCF;&#x4E2A; reducer &#x7684; <code>state</code> &#x53C2;&#x6570;&#x90FD;&#x4E0D;&#x540C;&#xFF0C;&#x5206;&#x522B;&#x5BF9;&#x5E94;&#x5B83;&#x7BA1;&#x7406;&#x7684;&#x90A3;&#x90E8;&#x5206; state &#x6570;&#x636E;&#x3002;</strong></p>
<p>&#x73B0;&#x5728;&#x770B;&#x8D77;&#x6765;&#x597D;&#x591A;&#x4E86;&#xFF01;&#x968F;&#x7740;&#x5E94;&#x7528;&#x7684;&#x81A8;&#x80C0;&#xFF0C;&#x6211;&#x4EEC;&#x8FD8;&#x53EF;&#x4EE5;&#x5C06;&#x62C6;&#x5206;&#x540E;&#x7684; reducer &#x653E;&#x5230;&#x4E0D;&#x540C;&#x7684;&#x6587;&#x4EF6;&#x4E2D;, &#x4EE5;&#x4FDD;&#x6301;&#x5176;&#x72EC;&#x7ACB;&#x6027;&#x5E76;&#x7528;&#x4E8E;&#x4E13;&#x95E8;&#x5904;&#x7406;&#x4E0D;&#x540C;&#x7684;&#x6570;&#x636E;&#x57DF;&#x3002;</p>
<p>&#x6700;&#x540E;&#xFF0C;Redux &#x63D0;&#x4F9B;&#x4E86; <a href="../api/combineReducers.html"><code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></a> &#x5DE5;&#x5177;&#x7C7B;&#x6765;&#x505A;&#x4E0A;&#x9762; <code>todoApp</code> &#x505A;&#x7684;&#x4E8B;&#x60C5;&#xFF0C;&#x8FD9;&#x6837;&#x5C31;&#x80FD;&#x6D88;&#x706D;&#x4E00;&#x4E9B;&#x6837;&#x677F;&#x4EE3;&#x7801;&#x4E86;&#x3002;&#x6709;&#x4E86;&#x5B83;&#xFF0C;&#x53EF;&#x4EE5;&#x8FD9;&#x6837;&#x91CD;&#x6784; <code>todoApp</code>&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> combineReducers <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> todoApp <span class="token operator">=</span> <span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  visibilityFilter<span class="token punctuation">,</span>
  todos
<span class="token punctuation">}</span><span class="token punctuation">)</span>

<span class="token keyword">export</span> <span class="token keyword">default</span> todoApp<span class="token punctuation">;</span>
</code></pre>
<p>&#x6CE8;&#x610F;&#x4E0A;&#x9762;&#x7684;&#x5199;&#x6CD5;&#x548C;&#x4E0B;&#x9762;&#x5B8C;&#x5168;&#x7B49;&#x4EF7;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token keyword">function</span> <span class="token function">todoApp</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">{</span>
    visibilityFilter<span class="token punctuation">:</span> <span class="token function">visibilityFilter</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>visibilityFilter<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    todos<span class="token punctuation">:</span> <span class="token function">todos</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>todos<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x4F60;&#x4E5F;&#x53EF;&#x4EE5;&#x7ED9;&#x5B83;&#x4EEC;&#x8BBE;&#x7F6E;&#x4E0D;&#x540C;&#x7684; key&#xFF0C;&#x6216;&#x8005;&#x8C03;&#x7528;&#x4E0D;&#x540C;&#x7684;&#x51FD;&#x6570;&#x3002;&#x4E0B;&#x9762;&#x4E24;&#x79CD;&#x5408;&#x6210; reducer &#x65B9;&#x6CD5;&#x5B8C;&#x5168;&#x7B49;&#x4EF7;&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">const</span> reducer <span class="token operator">=</span> <span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  a<span class="token punctuation">:</span> doSomethingWithA<span class="token punctuation">,</span>
  b<span class="token punctuation">:</span> processB<span class="token punctuation">,</span>
  c<span class="token punctuation">:</span> c
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre>
<pre><code class="lang-js"><span class="token keyword">function</span> <span class="token function">reducer</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">{</span>
    a<span class="token punctuation">:</span> <span class="token function">doSomethingWithA</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>a<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    b<span class="token punctuation">:</span> <span class="token function">processB</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>b<span class="token punctuation">,</span> action<span class="token punctuation">)</span><span class="token punctuation">,</span>
    c<span class="token punctuation">:</span> <span class="token function">c</span><span class="token punctuation">(</span>state<span class="token punctuation">.</span>c<span class="token punctuation">,</span> action<span class="token punctuation">)</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p><a href="../api/combineReducers.html"><code><span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">)</span></code></a> &#x6240;&#x505A;&#x7684;&#x53EA;&#x662F;&#x751F;&#x6210;&#x4E00;&#x4E2A;&#x51FD;&#x6570;&#xFF0C;&#x8FD9;&#x4E2A;&#x51FD;&#x6570;&#x6765;&#x8C03;&#x7528;&#x4F60;&#x7684;&#x4E00;&#x7CFB;&#x5217; reducer&#xFF0C;&#x6BCF;&#x4E2A; reducer <strong>&#x6839;&#x636E;&#x5B83;&#x4EEC;&#x7684; key &#x6765;&#x7B5B;&#x9009;&#x51FA; state &#x4E2D;&#x7684;&#x4E00;&#x90E8;&#x5206;&#x6570;&#x636E;&#x5E76;&#x5904;&#x7406;</strong>&#xFF0C;&#x7136;&#x540E;&#x8FD9;&#x4E2A;&#x751F;&#x6210;&#x7684;&#x51FD;&#x6570;&#x518D;&#x5C06;&#x6240;&#x6709; reducer &#x7684;&#x7ED3;&#x679C;&#x5408;&#x5E76;&#x6210;&#x4E00;&#x4E2A;&#x5927;&#x7684;&#x5BF9;&#x8C61;&#x3002;<a href="https://github.com/gaearon/redux/issues/428#issuecomment-129223274" target="_blank">&#x6CA1;&#x6709;&#x4EFB;&#x4F55;&#x9B54;&#x6CD5;&#x3002;</a></p>
<blockquote>
<h5 id="es6-%E7%94%A8%E6%88%B7%E4%BD%BF%E7%94%A8%E6%B3%A8%E6%84%8F">ES6 &#x7528;&#x6237;&#x4F7F;&#x7528;&#x6CE8;&#x610F;</h5>
<p><code>combineReducers</code> &#x63A5;&#x6536;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#xFF0C;&#x53EF;&#x4EE5;&#x628A;&#x6240;&#x6709;&#x9876;&#x7EA7;&#x7684; reducer &#x653E;&#x5230;&#x4E00;&#x4E2A;&#x72EC;&#x7ACB;&#x7684;&#x6587;&#x4EF6;&#x4E2D;&#xFF0C;&#x901A;&#x8FC7; <code><span class="token keyword">export</span></code> &#x66B4;&#x9732;&#x51FA;&#x6BCF;&#x4E2A; reducer &#x51FD;&#x6570;&#xFF0C;&#x7136;&#x540E;&#x4F7F;&#x7528; <code><span class="token keyword">import</span> <span class="token operator">*</span> as reducers</code> &#x5F97;&#x5230;&#x4E00;&#x4E2A;&#x4EE5;&#x5B83;&#x4EEC;&#x540D;&#x5B57;&#x4F5C;&#x4E3A; key &#x7684; object&#xFF1A;</p>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> combineReducers <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span>
<span class="token keyword">import</span> <span class="token operator">*</span> as reducers from <span class="token string">&apos;./reducers&apos;</span>

<span class="token keyword">const</span> todoApp <span class="token operator">=</span> <span class="token function">combineReducers</span><span class="token punctuation">(</span>reducers<span class="token punctuation">)</span>
</code></pre>
<p>&#x7531;&#x4E8E; <code><span class="token keyword">import</span> <span class="token operator">*</span></code> &#x8FD8;&#x662F;&#x6BD4;&#x8F83;&#x65B0;&#x7684;&#x8BED;&#x6CD5;&#xFF0C;&#x4E3A;&#x4E86;&#x907F;&#x514D;<a href="https://github.com/gaearon/redux/issues/428#issuecomment-129223274" target="_blank">&#x56F0;&#x60D1;</a>&#xFF0C;&#x6211;&#x4EEC;&#x4E0D;&#x4F1A;&#x5728;&#x672C;&#x6587;&#x6863;&#x4E2D;&#x4F7F;&#x7528;&#x5B83;&#x3002;&#x4F46;&#x5728;&#x4E00;&#x4E9B;&#x793E;&#x533A;&#x793A;&#x4F8B;&#x4E2D;&#x4F60;&#x53EF;&#x80FD;&#x4F1A;&#x9047;&#x5230;&#x5B83;&#x4EEC;&#x3002;</p>
</blockquote>
<h2 id="%E6%BA%90%E7%A0%81">&#x6E90;&#x7801;</h2>
<h4 id="-reducers-js"><code>reducers<span class="token punctuation">.</span>js</code></h4>
<pre><code class="lang-js"><span class="token keyword">import</span> <span class="token punctuation">{</span> combineReducers <span class="token punctuation">}</span> from <span class="token string">&apos;redux&apos;</span>
<span class="token keyword">import</span> <span class="token punctuation">{</span> ADD_TODO<span class="token punctuation">,</span> TOGGLE_TODO<span class="token punctuation">,</span> SET_VISIBILITY_FILTER<span class="token punctuation">,</span> VisibilityFilters <span class="token punctuation">}</span> from <span class="token string">&apos;./actions&apos;</span>
<span class="token keyword">const</span> <span class="token punctuation">{</span> SHOW_ALL <span class="token punctuation">}</span> <span class="token operator">=</span> VisibilityFilters

<span class="token keyword">function</span> <span class="token function">visibilityFilter</span><span class="token punctuation">(</span>state <span class="token operator">=</span> SHOW_ALL<span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> SET_VISIBILITY_FILTER<span class="token punctuation">:</span>
      <span class="token keyword">return</span> action<span class="token punctuation">.</span>filter
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">todos</span><span class="token punctuation">(</span>state <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">,</span> action<span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">switch</span> <span class="token punctuation">(</span>action<span class="token punctuation">.</span>type<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">case</span> ADD_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> <span class="token punctuation">[</span>
        <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>state<span class="token punctuation">,</span>
        <span class="token punctuation">{</span>
          text<span class="token punctuation">:</span> action<span class="token punctuation">.</span>text<span class="token punctuation">,</span>
          completed<span class="token punctuation">:</span> <span class="token keyword">false</span>
        <span class="token punctuation">}</span>
      <span class="token punctuation">]</span>
    <span class="token keyword">case</span> TOGGLE_TODO<span class="token punctuation">:</span>
      <span class="token keyword">return</span> state<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span>todo<span class="token punctuation">,</span> index<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>index <span class="token operator">===</span> action<span class="token punctuation">.</span>index<span class="token punctuation">)</span> <span class="token punctuation">{</span>
          <span class="token keyword">return</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> todo<span class="token punctuation">,</span> <span class="token punctuation">{</span>
            completed<span class="token punctuation">:</span> <span class="token operator">!</span>todo<span class="token punctuation">.</span>completed
          <span class="token punctuation">}</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
        <span class="token keyword">return</span> todo
      <span class="token punctuation">}</span><span class="token punctuation">)</span>
    <span class="token keyword">default</span><span class="token punctuation">:</span>
      <span class="token keyword">return</span> state
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">const</span> todoApp <span class="token operator">=</span> <span class="token function">combineReducers</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
  visibilityFilter<span class="token punctuation">,</span>
  todos
<span class="token punctuation">}</span><span class="token punctuation">)</span>

<span class="token keyword">export</span> <span class="token keyword">default</span> todoApp
</code></pre>
<h2 id="%E4%B8%8B%E4%B8%80%E6%AD%A5">&#x4E0B;&#x4E00;&#x6B65;</h2>
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